[linux.git] / net / sunrpc / xprt.c

/*
 *  linux/net/sunrpc/xprt.c
 *
 *  This is a generic RPC call interface supporting congestion avoidance,
 *  and asynchronous calls.
 *
 *  The interface works like this:
 *
 *  -   When a process places a call, it allocates a request slot if
 *      one is available. Otherwise, it sleeps on the backlog queue
 *      (xprt_reserve).
 *  -   Next, the caller puts together the RPC message, stuffs it into
 *      the request struct, and calls xprt_transmit().
 *  -   xprt_transmit sends the message and installs the caller on the
 *      transport's wait list. At the same time, if a reply is expected,
 *      it installs a timer that is run after the packet's timeout has
 *      expired.
 *  -   When a packet arrives, the data_ready handler walks the list of
 *      pending requests for that transport. If a matching XID is found, the
 *      caller is woken up, and the timer removed.
 *  -   When no reply arrives within the timeout interval, the timer is
 *      fired by the kernel and runs xprt_timer(). It either adjusts the
 *      timeout values (minor timeout) or wakes up the caller with a status
 *      of -ETIMEDOUT.
 *  -   When the caller receives a notification from RPC that a reply arrived,
 *      it should release the RPC slot, and process the reply.
 *      If the call timed out, it may choose to retry the operation by
 *      adjusting the initial timeout value, and simply calling rpc_call
 *      again.
 *
 *  Support for async RPC is done through a set of RPC-specific scheduling
 *  primitives that `transparently' work for processes as well as async
 *  tasks that rely on callbacks.
 *
 *  Copyright (C) 1995-1997, Olaf Kirch <okir@monad.swb.de>
 *
 *  Transport switch API copyright (C) 2005, Chuck Lever <cel@netapp.com>
 */

#include <linux/module.h>

#include <linux/types.h>
#include <linux/interrupt.h>
#include <linux/workqueue.h>
#include <linux/net.h>
#include <linux/ktime.h>

#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/metrics.h>
#include <linux/sunrpc/bc_xprt.h>
#include <linux/rcupdate.h>
#include <linux/sched/mm.h>

#include <trace/events/sunrpc.h>

#include "sunrpc.h"

/*
 * Local variables
 */

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
# define RPCDBG_FACILITY        RPCDBG_XPRT
#endif

/*
 * Local functions
 */
static void      xprt_init(struct rpc_xprt *xprt, struct net *net);
static __be32   xprt_alloc_xid(struct rpc_xprt *xprt);
static void      xprt_destroy(struct rpc_xprt *xprt);

static DEFINE_SPINLOCK(xprt_list_lock);
static LIST_HEAD(xprt_list);

static unsigned long xprt_request_timeout(const struct rpc_rqst *req)
{
        unsigned long timeout = jiffies + req->rq_timeout;

        if (time_before(timeout, req->rq_majortimeo))
                return timeout;
        return req->rq_majortimeo;
}

/**
 * xprt_register_transport - register a transport implementation
 * @transport: transport to register
 *
 * If a transport implementation is loaded as a kernel module, it can
 * call this interface to make itself known to the RPC client.
 *
 * Returns:
 * 0:           transport successfully registered
 * -EEXIST:     transport already registered
 * -EINVAL:     transport module being unloaded
 */
int xprt_register_transport(struct xprt_class *transport)
{
        struct xprt_class *t;
        int result;

        result = -EEXIST;
        spin_lock(&xprt_list_lock);
        list_for_each_entry(t, &xprt_list, list) {
                /* don't register the same transport class twice */
                if (t->ident == transport->ident)
                        goto out;
        }

        list_add_tail(&transport->list, &xprt_list);
        printk(KERN_INFO "RPC: Registered %s transport module.\n",
               transport->name);
        result = 0;

out:
        spin_unlock(&xprt_list_lock);
        return result;
}
EXPORT_SYMBOL_GPL(xprt_register_transport);

/**
 * xprt_unregister_transport - unregister a transport implementation
 * @transport: transport to unregister
 *
 * Returns:
 * 0:           transport successfully unregistered
 * -ENOENT:     transport never registered
 */
int xprt_unregister_transport(struct xprt_class *transport)
{
        struct xprt_class *t;
        int result;

        result = 0;
        spin_lock(&xprt_list_lock);
        list_for_each_entry(t, &xprt_list, list) {
                if (t == transport) {
                        printk(KERN_INFO
                                "RPC: Unregistered %s transport module.\n",
                                transport->name);
                        list_del_init(&transport->list);
                        goto out;
                }
        }
        result = -ENOENT;

out:
        spin_unlock(&xprt_list_lock);
        return result;
}
EXPORT_SYMBOL_GPL(xprt_unregister_transport);

/**
 * xprt_load_transport - load a transport implementation
 * @transport_name: transport to load
 *
 * Returns:
 * 0:           transport successfully loaded
 * -ENOENT:     transport module not available
 */
int xprt_load_transport(const char *transport_name)
{
        struct xprt_class *t;
        int result;

        result = 0;
        spin_lock(&xprt_list_lock);
        list_for_each_entry(t, &xprt_list, list) {
                if (strcmp(t->name, transport_name) == 0) {
                        spin_unlock(&xprt_list_lock);
                        goto out;
                }
        }
        spin_unlock(&xprt_list_lock);
        result = request_module("xprt%s", transport_name);
out:
        return result;
}
EXPORT_SYMBOL_GPL(xprt_load_transport);

static void xprt_clear_locked(struct rpc_xprt *xprt)
{
        xprt->snd_task = NULL;
        if (!test_bit(XPRT_CLOSE_WAIT, &xprt->state)) {
                smp_mb__before_atomic();
                clear_bit(XPRT_LOCKED, &xprt->state);
                smp_mb__after_atomic();
        } else
                queue_work(xprtiod_workqueue, &xprt->task_cleanup);
}

/**
 * xprt_reserve_xprt - serialize write access to transports
 * @task: task that is requesting access to the transport
 * @xprt: pointer to the target transport
 *
 * This prevents mixing the payload of separate requests, and prevents
 * transport connects from colliding with writes.  No congestion control
 * is provided.
 */
int xprt_reserve_xprt(struct rpc_xprt *xprt, struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;

        if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
                if (task == xprt->snd_task)
                        return 1;
                goto out_sleep;
        }
        if (test_bit(XPRT_WRITE_SPACE, &xprt->state))
                goto out_unlock;
        xprt->snd_task = task;

        return 1;

out_unlock:
        xprt_clear_locked(xprt);
out_sleep:
        dprintk("RPC: %5u failed to lock transport %p\n",
                        task->tk_pid, xprt);
        task->tk_status = -EAGAIN;
        if  (RPC_IS_SOFT(task))
                rpc_sleep_on_timeout(&xprt->sending, task, NULL,
                                xprt_request_timeout(req));
        else
                rpc_sleep_on(&xprt->sending, task, NULL);
        return 0;
}
EXPORT_SYMBOL_GPL(xprt_reserve_xprt);

static bool
xprt_need_congestion_window_wait(struct rpc_xprt *xprt)
{
        return test_bit(XPRT_CWND_WAIT, &xprt->state);
}

static void
xprt_set_congestion_window_wait(struct rpc_xprt *xprt)
{
        if (!list_empty(&xprt->xmit_queue)) {
                /* Peek at head of queue to see if it can make progress */
                if (list_first_entry(&xprt->xmit_queue, struct rpc_rqst,
                                        rq_xmit)->rq_cong)
                        return;
        }
        set_bit(XPRT_CWND_WAIT, &xprt->state);
}

static void
xprt_test_and_clear_congestion_window_wait(struct rpc_xprt *xprt)
{
        if (!RPCXPRT_CONGESTED(xprt))
                clear_bit(XPRT_CWND_WAIT, &xprt->state);
}

/*
 * xprt_reserve_xprt_cong - serialize write access to transports
 * @task: task that is requesting access to the transport
 *
 * Same as xprt_reserve_xprt, but Van Jacobson congestion control is
 * integrated into the decision of whether a request is allowed to be
 * woken up and given access to the transport.
 * Note that the lock is only granted if we know there are free slots.
 */
int xprt_reserve_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;

        if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
                if (task == xprt->snd_task)
                        return 1;
                goto out_sleep;
        }
        if (req == NULL) {
                xprt->snd_task = task;
                return 1;
        }
        if (test_bit(XPRT_WRITE_SPACE, &xprt->state))
                goto out_unlock;
        if (!xprt_need_congestion_window_wait(xprt)) {
                xprt->snd_task = task;
                return 1;
        }
out_unlock:
        xprt_clear_locked(xprt);
out_sleep:
        dprintk("RPC: %5u failed to lock transport %p\n", task->tk_pid, xprt);
        task->tk_status = -EAGAIN;
        if (RPC_IS_SOFT(task))
                rpc_sleep_on_timeout(&xprt->sending, task, NULL,
                                xprt_request_timeout(req));
        else
                rpc_sleep_on(&xprt->sending, task, NULL);
        return 0;
}
EXPORT_SYMBOL_GPL(xprt_reserve_xprt_cong);

static inline int xprt_lock_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
        int retval;

        if (test_bit(XPRT_LOCKED, &xprt->state) && xprt->snd_task == task)
                return 1;
        spin_lock_bh(&xprt->transport_lock);
        retval = xprt->ops->reserve_xprt(xprt, task);
        spin_unlock_bh(&xprt->transport_lock);
        return retval;
}

static bool __xprt_lock_write_func(struct rpc_task *task, void *data)
{
        struct rpc_xprt *xprt = data;

        xprt->snd_task = task;
        return true;
}

static void __xprt_lock_write_next(struct rpc_xprt *xprt)
{
        if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
                return;
        if (test_bit(XPRT_WRITE_SPACE, &xprt->state))
                goto out_unlock;
        if (rpc_wake_up_first_on_wq(xprtiod_workqueue, &xprt->sending,
                                __xprt_lock_write_func, xprt))
                return;
out_unlock:
        xprt_clear_locked(xprt);
}

static void __xprt_lock_write_next_cong(struct rpc_xprt *xprt)
{
        if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
                return;
        if (test_bit(XPRT_WRITE_SPACE, &xprt->state))
                goto out_unlock;
        if (xprt_need_congestion_window_wait(xprt))
                goto out_unlock;
        if (rpc_wake_up_first_on_wq(xprtiod_workqueue, &xprt->sending,
                                __xprt_lock_write_func, xprt))
                return;
out_unlock:
        xprt_clear_locked(xprt);
}

/**
 * xprt_release_xprt - allow other requests to use a transport
 * @xprt: transport with other tasks potentially waiting
 * @task: task that is releasing access to the transport
 *
 * Note that "task" can be NULL.  No congestion control is provided.
 */
void xprt_release_xprt(struct rpc_xprt *xprt, struct rpc_task *task)
{
        if (xprt->snd_task == task) {
                xprt_clear_locked(xprt);
                __xprt_lock_write_next(xprt);
        }
}
EXPORT_SYMBOL_GPL(xprt_release_xprt);

/**
 * xprt_release_xprt_cong - allow other requests to use a transport
 * @xprt: transport with other tasks potentially waiting
 * @task: task that is releasing access to the transport
 *
 * Note that "task" can be NULL.  Another task is awoken to use the
 * transport if the transport's congestion window allows it.
 */
void xprt_release_xprt_cong(struct rpc_xprt *xprt, struct rpc_task *task)
{
        if (xprt->snd_task == task) {
                xprt_clear_locked(xprt);
                __xprt_lock_write_next_cong(xprt);
        }
}
EXPORT_SYMBOL_GPL(xprt_release_xprt_cong);

static inline void xprt_release_write(struct rpc_xprt *xprt, struct rpc_task *task)
{
        if (xprt->snd_task != task)
                return;
        spin_lock_bh(&xprt->transport_lock);
        xprt->ops->release_xprt(xprt, task);
        spin_unlock_bh(&xprt->transport_lock);
}

/*
 * Van Jacobson congestion avoidance. Check if the congestion window
 * overflowed. Put the task to sleep if this is the case.
 */
static int
__xprt_get_cong(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
        if (req->rq_cong)
                return 1;
        dprintk("RPC: %5u xprt_cwnd_limited cong = %lu cwnd = %lu\n",
                        req->rq_task->tk_pid, xprt->cong, xprt->cwnd);
        if (RPCXPRT_CONGESTED(xprt)) {
                xprt_set_congestion_window_wait(xprt);
                return 0;
        }
        req->rq_cong = 1;
        xprt->cong += RPC_CWNDSCALE;
        return 1;
}

/*
 * Adjust the congestion window, and wake up the next task
 * that has been sleeping due to congestion
 */
static void
__xprt_put_cong(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
        if (!req->rq_cong)
                return;
        req->rq_cong = 0;
        xprt->cong -= RPC_CWNDSCALE;
        xprt_test_and_clear_congestion_window_wait(xprt);
        __xprt_lock_write_next_cong(xprt);
}

/**
 * xprt_request_get_cong - Request congestion control credits
 * @xprt: pointer to transport
 * @req: pointer to RPC request
 *
 * Useful for transports that require congestion control.
 */
bool
xprt_request_get_cong(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
        bool ret = false;

        if (req->rq_cong)
                return true;
        spin_lock_bh(&xprt->transport_lock);
        ret = __xprt_get_cong(xprt, req) != 0;
        spin_unlock_bh(&xprt->transport_lock);
        return ret;
}
EXPORT_SYMBOL_GPL(xprt_request_get_cong);

/**
 * xprt_release_rqst_cong - housekeeping when request is complete
 * @task: RPC request that recently completed
 *
 * Useful for transports that require congestion control.
 */
void xprt_release_rqst_cong(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;

        __xprt_put_cong(req->rq_xprt, req);
}
EXPORT_SYMBOL_GPL(xprt_release_rqst_cong);

/*
 * Clear the congestion window wait flag and wake up the next
 * entry on xprt->sending
 */
static void
xprt_clear_congestion_window_wait(struct rpc_xprt *xprt)
{
        if (test_and_clear_bit(XPRT_CWND_WAIT, &xprt->state)) {
                spin_lock_bh(&xprt->transport_lock);
                __xprt_lock_write_next_cong(xprt);
                spin_unlock_bh(&xprt->transport_lock);
        }
}

/**
 * xprt_adjust_cwnd - adjust transport congestion window
 * @xprt: pointer to xprt
 * @task: recently completed RPC request used to adjust window
 * @result: result code of completed RPC request
 *
 * The transport code maintains an estimate on the maximum number of out-
 * standing RPC requests, using a smoothed version of the congestion
 * avoidance implemented in 44BSD. This is basically the Van Jacobson
 * congestion algorithm: If a retransmit occurs, the congestion window is
 * halved; otherwise, it is incremented by 1/cwnd when
 *
 *      -       a reply is received and
 *      -       a full number of requests are outstanding and
 *      -       the congestion window hasn't been updated recently.
 */
void xprt_adjust_cwnd(struct rpc_xprt *xprt, struct rpc_task *task, int result)
{
        struct rpc_rqst *req = task->tk_rqstp;
        unsigned long cwnd = xprt->cwnd;

        if (result >= 0 && cwnd <= xprt->cong) {
                /* The (cwnd >> 1) term makes sure
                 * the result gets rounded properly. */
                cwnd += (RPC_CWNDSCALE * RPC_CWNDSCALE + (cwnd >> 1)) / cwnd;
                if (cwnd > RPC_MAXCWND(xprt))
                        cwnd = RPC_MAXCWND(xprt);
                __xprt_lock_write_next_cong(xprt);
        } else if (result == -ETIMEDOUT) {
                cwnd >>= 1;
                if (cwnd < RPC_CWNDSCALE)
                        cwnd = RPC_CWNDSCALE;
        }
        dprintk("RPC:       cong %ld, cwnd was %ld, now %ld\n",
                        xprt->cong, xprt->cwnd, cwnd);
        xprt->cwnd = cwnd;
        __xprt_put_cong(xprt, req);
}
EXPORT_SYMBOL_GPL(xprt_adjust_cwnd);

/**
 * xprt_wake_pending_tasks - wake all tasks on a transport's pending queue
 * @xprt: transport with waiting tasks
 * @status: result code to plant in each task before waking it
 *
 */
void xprt_wake_pending_tasks(struct rpc_xprt *xprt, int status)
{
        if (status < 0)
                rpc_wake_up_status(&xprt->pending, status);
        else
                rpc_wake_up(&xprt->pending);
}
EXPORT_SYMBOL_GPL(xprt_wake_pending_tasks);

/**
 * xprt_wait_for_buffer_space - wait for transport output buffer to clear
 * @xprt: transport
 *
 * Note that we only set the timer for the case of RPC_IS_SOFT(), since
 * we don't in general want to force a socket disconnection due to
 * an incomplete RPC call transmission.
 */
void xprt_wait_for_buffer_space(struct rpc_xprt *xprt)
{
        set_bit(XPRT_WRITE_SPACE, &xprt->state);
}
EXPORT_SYMBOL_GPL(xprt_wait_for_buffer_space);

static bool
xprt_clear_write_space_locked(struct rpc_xprt *xprt)
{
        if (test_and_clear_bit(XPRT_WRITE_SPACE, &xprt->state)) {
                __xprt_lock_write_next(xprt);
                dprintk("RPC:       write space: waking waiting task on "
                                "xprt %p\n", xprt);
                return true;
        }
        return false;
}

/**
 * xprt_write_space - wake the task waiting for transport output buffer space
 * @xprt: transport with waiting tasks
 *
 * Can be called in a soft IRQ context, so xprt_write_space never sleeps.
 */
bool xprt_write_space(struct rpc_xprt *xprt)
{
        bool ret;

        if (!test_bit(XPRT_WRITE_SPACE, &xprt->state))
                return false;
        spin_lock_bh(&xprt->transport_lock);
        ret = xprt_clear_write_space_locked(xprt);
        spin_unlock_bh(&xprt->transport_lock);
        return ret;
}
EXPORT_SYMBOL_GPL(xprt_write_space);

static void xprt_reset_majortimeo(struct rpc_rqst *req)
{
        const struct rpc_timeout *to = req->rq_task->tk_client->cl_timeout;

        req->rq_majortimeo = req->rq_timeout;
        if (to->to_exponential)
                req->rq_majortimeo <<= to->to_retries;
        else
                req->rq_majortimeo += to->to_increment * to->to_retries;
        if (req->rq_majortimeo > to->to_maxval || req->rq_majortimeo == 0)
                req->rq_majortimeo = to->to_maxval;
        req->rq_majortimeo += jiffies;
}

/**
 * xprt_adjust_timeout - adjust timeout values for next retransmit
 * @req: RPC request containing parameters to use for the adjustment
 *
 */
int xprt_adjust_timeout(struct rpc_rqst *req)
{
        struct rpc_xprt *xprt = req->rq_xprt;
        const struct rpc_timeout *to = req->rq_task->tk_client->cl_timeout;
        int status = 0;

        if (time_before(jiffies, req->rq_majortimeo)) {
                if (to->to_exponential)
                        req->rq_timeout <<= 1;
                else
                        req->rq_timeout += to->to_increment;
                if (to->to_maxval && req->rq_timeout >= to->to_maxval)
                        req->rq_timeout = to->to_maxval;
                req->rq_retries++;
        } else {
                req->rq_timeout = to->to_initval;
                req->rq_retries = 0;
                xprt_reset_majortimeo(req);
                /* Reset the RTT counters == "slow start" */
                spin_lock_bh(&xprt->transport_lock);
                rpc_init_rtt(req->rq_task->tk_client->cl_rtt, to->to_initval);
                spin_unlock_bh(&xprt->transport_lock);
                status = -ETIMEDOUT;
        }

        if (req->rq_timeout == 0) {
                printk(KERN_WARNING "xprt_adjust_timeout: rq_timeout = 0!\n");
                req->rq_timeout = 5 * HZ;
        }
        return status;
}

static void xprt_autoclose(struct work_struct *work)
{
        struct rpc_xprt *xprt =
                container_of(work, struct rpc_xprt, task_cleanup);
        unsigned int pflags = memalloc_nofs_save();

        clear_bit(XPRT_CLOSE_WAIT, &xprt->state);
        xprt->ops->close(xprt);
        xprt_release_write(xprt, NULL);
        wake_up_bit(&xprt->state, XPRT_LOCKED);
        memalloc_nofs_restore(pflags);
}

/**
 * xprt_disconnect_done - mark a transport as disconnected
 * @xprt: transport to flag for disconnect
 *
 */
void xprt_disconnect_done(struct rpc_xprt *xprt)
{
        dprintk("RPC:       disconnected transport %p\n", xprt);
        spin_lock_bh(&xprt->transport_lock);
        xprt_clear_connected(xprt);
        xprt_clear_write_space_locked(xprt);
        xprt_wake_pending_tasks(xprt, -ENOTCONN);
        spin_unlock_bh(&xprt->transport_lock);
}
EXPORT_SYMBOL_GPL(xprt_disconnect_done);

/**
 * xprt_force_disconnect - force a transport to disconnect
 * @xprt: transport to disconnect
 *
 */
void xprt_force_disconnect(struct rpc_xprt *xprt)
{
        /* Don't race with the test_bit() in xprt_clear_locked() */
        spin_lock_bh(&xprt->transport_lock);
        set_bit(XPRT_CLOSE_WAIT, &xprt->state);
        /* Try to schedule an autoclose RPC call */
        if (test_and_set_bit(XPRT_LOCKED, &xprt->state) == 0)
                queue_work(xprtiod_workqueue, &xprt->task_cleanup);
        else if (xprt->snd_task)
                rpc_wake_up_queued_task_set_status(&xprt->pending,
                                xprt->snd_task, -ENOTCONN);
        spin_unlock_bh(&xprt->transport_lock);
}
EXPORT_SYMBOL_GPL(xprt_force_disconnect);

static unsigned int
xprt_connect_cookie(struct rpc_xprt *xprt)
{
        return READ_ONCE(xprt->connect_cookie);
}

static bool
xprt_request_retransmit_after_disconnect(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        return req->rq_connect_cookie != xprt_connect_cookie(xprt) ||
                !xprt_connected(xprt);
}

/**
 * xprt_conditional_disconnect - force a transport to disconnect
 * @xprt: transport to disconnect
 * @cookie: 'connection cookie'
 *
 * This attempts to break the connection if and only if 'cookie' matches
 * the current transport 'connection cookie'. It ensures that we don't
 * try to break the connection more than once when we need to retransmit
 * a batch of RPC requests.
 *
 */
void xprt_conditional_disconnect(struct rpc_xprt *xprt, unsigned int cookie)
{
        /* Don't race with the test_bit() in xprt_clear_locked() */
        spin_lock_bh(&xprt->transport_lock);
        if (cookie != xprt->connect_cookie)
                goto out;
        if (test_bit(XPRT_CLOSING, &xprt->state))
                goto out;
        set_bit(XPRT_CLOSE_WAIT, &xprt->state);
        /* Try to schedule an autoclose RPC call */
        if (test_and_set_bit(XPRT_LOCKED, &xprt->state) == 0)
                queue_work(xprtiod_workqueue, &xprt->task_cleanup);
        xprt_wake_pending_tasks(xprt, -EAGAIN);
out:
        spin_unlock_bh(&xprt->transport_lock);
}

static bool
xprt_has_timer(const struct rpc_xprt *xprt)
{
        return xprt->idle_timeout != 0;
}

static void
xprt_schedule_autodisconnect(struct rpc_xprt *xprt)
        __must_hold(&xprt->transport_lock)
{
        if (RB_EMPTY_ROOT(&xprt->recv_queue) && xprt_has_timer(xprt))
                mod_timer(&xprt->timer, xprt->last_used + xprt->idle_timeout);
}

static void
xprt_init_autodisconnect(struct timer_list *t)
{
        struct rpc_xprt *xprt = from_timer(xprt, t, timer);

        spin_lock(&xprt->transport_lock);
        if (!RB_EMPTY_ROOT(&xprt->recv_queue))
                goto out_abort;
        /* Reset xprt->last_used to avoid connect/autodisconnect cycling */
        xprt->last_used = jiffies;
        if (test_and_set_bit(XPRT_LOCKED, &xprt->state))
                goto out_abort;
        spin_unlock(&xprt->transport_lock);
        queue_work(xprtiod_workqueue, &xprt->task_cleanup);
        return;
out_abort:
        spin_unlock(&xprt->transport_lock);
}

bool xprt_lock_connect(struct rpc_xprt *xprt,
                struct rpc_task *task,
                void *cookie)
{
        bool ret = false;

        spin_lock_bh(&xprt->transport_lock);
        if (!test_bit(XPRT_LOCKED, &xprt->state))
                goto out;
        if (xprt->snd_task != task)
                goto out;
        xprt->snd_task = cookie;
        ret = true;
out:
        spin_unlock_bh(&xprt->transport_lock);
        return ret;
}

void xprt_unlock_connect(struct rpc_xprt *xprt, void *cookie)
{
        spin_lock_bh(&xprt->transport_lock);
        if (xprt->snd_task != cookie)
                goto out;
        if (!test_bit(XPRT_LOCKED, &xprt->state))
                goto out;
        xprt->snd_task =NULL;
        xprt->ops->release_xprt(xprt, NULL);
        xprt_schedule_autodisconnect(xprt);
out:
        spin_unlock_bh(&xprt->transport_lock);
        wake_up_bit(&xprt->state, XPRT_LOCKED);
}

/**
 * xprt_connect - schedule a transport connect operation
 * @task: RPC task that is requesting the connect
 *
 */
void xprt_connect(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_rqstp->rq_xprt;

        dprintk("RPC: %5u xprt_connect xprt %p %s connected\n", task->tk_pid,
                        xprt, (xprt_connected(xprt) ? "is" : "is not"));

        if (!xprt_bound(xprt)) {
                task->tk_status = -EAGAIN;
                return;
        }
        if (!xprt_lock_write(xprt, task))
                return;

        if (test_and_clear_bit(XPRT_CLOSE_WAIT, &xprt->state))
                xprt->ops->close(xprt);

        if (!xprt_connected(xprt)) {
                task->tk_rqstp->rq_connect_cookie = xprt->connect_cookie;
                rpc_sleep_on_timeout(&xprt->pending, task, NULL,
                                xprt_request_timeout(task->tk_rqstp));

                if (test_bit(XPRT_CLOSING, &xprt->state))
                        return;
                if (xprt_test_and_set_connecting(xprt))
                        return;
                /* Race breaker */
                if (!xprt_connected(xprt)) {
                        xprt->stat.connect_start = jiffies;
                        xprt->ops->connect(xprt, task);
                } else {
                        xprt_clear_connecting(xprt);
                        task->tk_status = 0;
                        rpc_wake_up_queued_task(&xprt->pending, task);
                }
        }
        xprt_release_write(xprt, task);
}

enum xprt_xid_rb_cmp {
        XID_RB_EQUAL,
        XID_RB_LEFT,
        XID_RB_RIGHT,
};
static enum xprt_xid_rb_cmp
xprt_xid_cmp(__be32 xid1, __be32 xid2)
{
        if (xid1 == xid2)
                return XID_RB_EQUAL;
        if ((__force u32)xid1 < (__force u32)xid2)
                return XID_RB_LEFT;
        return XID_RB_RIGHT;
}

static struct rpc_rqst *
xprt_request_rb_find(struct rpc_xprt *xprt, __be32 xid)
{
        struct rb_node *n = xprt->recv_queue.rb_node;
        struct rpc_rqst *req;

        while (n != NULL) {
                req = rb_entry(n, struct rpc_rqst, rq_recv);
                switch (xprt_xid_cmp(xid, req->rq_xid)) {
                case XID_RB_LEFT:
                        n = n->rb_left;
                        break;
                case XID_RB_RIGHT:
                        n = n->rb_right;
                        break;
                case XID_RB_EQUAL:
                        return req;
                }
        }
        return NULL;
}

static void
xprt_request_rb_insert(struct rpc_xprt *xprt, struct rpc_rqst *new)
{
        struct rb_node **p = &xprt->recv_queue.rb_node;
        struct rb_node *n = NULL;
        struct rpc_rqst *req;

        while (*p != NULL) {
                n = *p;
                req = rb_entry(n, struct rpc_rqst, rq_recv);
                switch(xprt_xid_cmp(new->rq_xid, req->rq_xid)) {
                case XID_RB_LEFT:
                        p = &n->rb_left;
                        break;
                case XID_RB_RIGHT:
                        p = &n->rb_right;
                        break;
                case XID_RB_EQUAL:
                        WARN_ON_ONCE(new != req);
                        return;
                }
        }
        rb_link_node(&new->rq_recv, n, p);
        rb_insert_color(&new->rq_recv, &xprt->recv_queue);
}

static void
xprt_request_rb_remove(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
        rb_erase(&req->rq_recv, &xprt->recv_queue);
}

/**
 * xprt_lookup_rqst - find an RPC request corresponding to an XID
 * @xprt: transport on which the original request was transmitted
 * @xid: RPC XID of incoming reply
 *
 * Caller holds xprt->queue_lock.
 */
struct rpc_rqst *xprt_lookup_rqst(struct rpc_xprt *xprt, __be32 xid)
{
        struct rpc_rqst *entry;

        entry = xprt_request_rb_find(xprt, xid);
        if (entry != NULL) {
                trace_xprt_lookup_rqst(xprt, xid, 0);
                entry->rq_rtt = ktime_sub(ktime_get(), entry->rq_xtime);
                return entry;
        }

        dprintk("RPC:       xprt_lookup_rqst did not find xid %08x\n",
                        ntohl(xid));
        trace_xprt_lookup_rqst(xprt, xid, -ENOENT);
        xprt->stat.bad_xids++;
        return NULL;
}
EXPORT_SYMBOL_GPL(xprt_lookup_rqst);

static bool
xprt_is_pinned_rqst(struct rpc_rqst *req)
{
        return atomic_read(&req->rq_pin) != 0;
}

/**
 * xprt_pin_rqst - Pin a request on the transport receive list
 * @req: Request to pin
 *
 * Caller must ensure this is atomic with the call to xprt_lookup_rqst()
 * so should be holding the xprt receive lock.
 */
void xprt_pin_rqst(struct rpc_rqst *req)
{
        atomic_inc(&req->rq_pin);
}
EXPORT_SYMBOL_GPL(xprt_pin_rqst);

/**
 * xprt_unpin_rqst - Unpin a request on the transport receive list
 * @req: Request to pin
 *
 * Caller should be holding the xprt receive lock.
 */
void xprt_unpin_rqst(struct rpc_rqst *req)
{
        if (!test_bit(RPC_TASK_MSG_PIN_WAIT, &req->rq_task->tk_runstate)) {
                atomic_dec(&req->rq_pin);
                return;
        }
        if (atomic_dec_and_test(&req->rq_pin))
                wake_up_var(&req->rq_pin);
}
EXPORT_SYMBOL_GPL(xprt_unpin_rqst);

static void xprt_wait_on_pinned_rqst(struct rpc_rqst *req)
{
        wait_var_event(&req->rq_pin, !xprt_is_pinned_rqst(req));
}

static bool
xprt_request_data_received(struct rpc_task *task)
{
        return !test_bit(RPC_TASK_NEED_RECV, &task->tk_runstate) &&
                READ_ONCE(task->tk_rqstp->rq_reply_bytes_recvd) != 0;
}

static bool
xprt_request_need_enqueue_receive(struct rpc_task *task, struct rpc_rqst *req)
{
        return !test_bit(RPC_TASK_NEED_RECV, &task->tk_runstate) &&
                READ_ONCE(task->tk_rqstp->rq_reply_bytes_recvd) == 0;
}

/**
 * xprt_request_enqueue_receive - Add an request to the receive queue
 * @task: RPC task
 *
 */
void
xprt_request_enqueue_receive(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        if (!xprt_request_need_enqueue_receive(task, req))
                return;
        spin_lock(&xprt->queue_lock);

        /* Update the softirq receive buffer */
        memcpy(&req->rq_private_buf, &req->rq_rcv_buf,
                        sizeof(req->rq_private_buf));

        /* Add request to the receive list */
        xprt_request_rb_insert(xprt, req);
        set_bit(RPC_TASK_NEED_RECV, &task->tk_runstate);
        spin_unlock(&xprt->queue_lock);

        xprt_reset_majortimeo(req);
        /* Turn off autodisconnect */
        del_singleshot_timer_sync(&xprt->timer);
}

/**
 * xprt_request_dequeue_receive_locked - Remove a request from the receive queue
 * @task: RPC task
 *
 * Caller must hold xprt->queue_lock.
 */
static void
xprt_request_dequeue_receive_locked(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;

        if (test_and_clear_bit(RPC_TASK_NEED_RECV, &task->tk_runstate))
                xprt_request_rb_remove(req->rq_xprt, req);
}

/**
 * xprt_update_rtt - Update RPC RTT statistics
 * @task: RPC request that recently completed
 *
 * Caller holds xprt->queue_lock.
 */
void xprt_update_rtt(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_rtt *rtt = task->tk_client->cl_rtt;
        unsigned int timer = task->tk_msg.rpc_proc->p_timer;
        long m = usecs_to_jiffies(ktime_to_us(req->rq_rtt));

        if (timer) {
                if (req->rq_ntrans == 1)
                        rpc_update_rtt(rtt, timer, m);
                rpc_set_timeo(rtt, timer, req->rq_ntrans - 1);
        }
}
EXPORT_SYMBOL_GPL(xprt_update_rtt);

/**
 * xprt_complete_rqst - called when reply processing is complete
 * @task: RPC request that recently completed
 * @copied: actual number of bytes received from the transport
 *
 * Caller holds xprt->queue_lock.
 */
void xprt_complete_rqst(struct rpc_task *task, int copied)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        dprintk("RPC: %5u xid %08x complete (%d bytes received)\n",
                        task->tk_pid, ntohl(req->rq_xid), copied);
        trace_xprt_complete_rqst(xprt, req->rq_xid, copied);

        xprt->stat.recvs++;

        req->rq_private_buf.len = copied;
        /* Ensure all writes are done before we update */
        /* req->rq_reply_bytes_recvd */
        smp_wmb();
        req->rq_reply_bytes_recvd = copied;
        xprt_request_dequeue_receive_locked(task);
        rpc_wake_up_queued_task(&xprt->pending, task);
}
EXPORT_SYMBOL_GPL(xprt_complete_rqst);

static void xprt_timer(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        if (task->tk_status != -ETIMEDOUT)
                return;

        trace_xprt_timer(xprt, req->rq_xid, task->tk_status);
        if (!req->rq_reply_bytes_recvd) {
                if (xprt->ops->timer)
                        xprt->ops->timer(xprt, task);
        } else
                task->tk_status = 0;
}

/**
 * xprt_wait_for_reply_request_def - wait for reply
 * @task: pointer to rpc_task
 *
 * Set a request's retransmit timeout based on the transport's
 * default timeout parameters.  Used by transports that don't adjust
 * the retransmit timeout based on round-trip time estimation,
 * and put the task to sleep on the pending queue.
 */
void xprt_wait_for_reply_request_def(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;

        rpc_sleep_on_timeout(&req->rq_xprt->pending, task, xprt_timer,
                        xprt_request_timeout(req));
}
EXPORT_SYMBOL_GPL(xprt_wait_for_reply_request_def);

/**
 * xprt_wait_for_reply_request_rtt - wait for reply using RTT estimator
 * @task: pointer to rpc_task
 *
 * Set a request's retransmit timeout using the RTT estimator,
 * and put the task to sleep on the pending queue.
 */
void xprt_wait_for_reply_request_rtt(struct rpc_task *task)
{
        int timer = task->tk_msg.rpc_proc->p_timer;
        struct rpc_clnt *clnt = task->tk_client;
        struct rpc_rtt *rtt = clnt->cl_rtt;
        struct rpc_rqst *req = task->tk_rqstp;
        unsigned long max_timeout = clnt->cl_timeout->to_maxval;
        unsigned long timeout;

        timeout = rpc_calc_rto(rtt, timer);
        timeout <<= rpc_ntimeo(rtt, timer) + req->rq_retries;
        if (timeout > max_timeout || timeout == 0)
                timeout = max_timeout;
        rpc_sleep_on_timeout(&req->rq_xprt->pending, task, xprt_timer,
                        jiffies + timeout);
}
EXPORT_SYMBOL_GPL(xprt_wait_for_reply_request_rtt);

/**
 * xprt_request_wait_receive - wait for the reply to an RPC request
 * @task: RPC task about to send a request
 *
 */
void xprt_request_wait_receive(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        if (!test_bit(RPC_TASK_NEED_RECV, &task->tk_runstate))
                return;
        /*
         * Sleep on the pending queue if we're expecting a reply.
         * The spinlock ensures atomicity between the test of
         * req->rq_reply_bytes_recvd, and the call to rpc_sleep_on().
         */
        spin_lock(&xprt->queue_lock);
        if (test_bit(RPC_TASK_NEED_RECV, &task->tk_runstate)) {
                xprt->ops->wait_for_reply_request(task);
                /*
                 * Send an extra queue wakeup call if the
                 * connection was dropped in case the call to
                 * rpc_sleep_on() raced.
                 */
                if (xprt_request_retransmit_after_disconnect(task))
                        rpc_wake_up_queued_task_set_status(&xprt->pending,
                                        task, -ENOTCONN);
        }
        spin_unlock(&xprt->queue_lock);
}

static bool
xprt_request_need_enqueue_transmit(struct rpc_task *task, struct rpc_rqst *req)
{
        return !test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate);
}

/**
 * xprt_request_enqueue_transmit - queue a task for transmission
 * @task: pointer to rpc_task
 *
 * Add a task to the transmission queue.
 */
void
xprt_request_enqueue_transmit(struct rpc_task *task)
{
        struct rpc_rqst *pos, *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        if (xprt_request_need_enqueue_transmit(task, req)) {
                req->rq_bytes_sent = 0;
                spin_lock(&xprt->queue_lock);
                /*
                 * Requests that carry congestion control credits are added
                 * to the head of the list to avoid starvation issues.
                 */
                if (req->rq_cong) {
                        xprt_clear_congestion_window_wait(xprt);
                        list_for_each_entry(pos, &xprt->xmit_queue, rq_xmit) {
                                if (pos->rq_cong)
                                        continue;
                                /* Note: req is added _before_ pos */
                                list_add_tail(&req->rq_xmit, &pos->rq_xmit);
                                INIT_LIST_HEAD(&req->rq_xmit2);
                                trace_xprt_enq_xmit(task, 1);
                                goto out;
                        }
                } else if (RPC_IS_SWAPPER(task)) {
                        list_for_each_entry(pos, &xprt->xmit_queue, rq_xmit) {
                                if (pos->rq_cong || pos->rq_bytes_sent)
                                        continue;
                                if (RPC_IS_SWAPPER(pos->rq_task))
                                        continue;
                                /* Note: req is added _before_ pos */
                                list_add_tail(&req->rq_xmit, &pos->rq_xmit);
                                INIT_LIST_HEAD(&req->rq_xmit2);
                                trace_xprt_enq_xmit(task, 2);
                                goto out;
                        }
                } else if (!req->rq_seqno) {
                        list_for_each_entry(pos, &xprt->xmit_queue, rq_xmit) {
                                if (pos->rq_task->tk_owner != task->tk_owner)
                                        continue;
                                list_add_tail(&req->rq_xmit2, &pos->rq_xmit2);
                                INIT_LIST_HEAD(&req->rq_xmit);
                                trace_xprt_enq_xmit(task, 3);
                                goto out;
                        }
                }
                list_add_tail(&req->rq_xmit, &xprt->xmit_queue);
                INIT_LIST_HEAD(&req->rq_xmit2);
                trace_xprt_enq_xmit(task, 4);
out:
                set_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate);
                spin_unlock(&xprt->queue_lock);
        }
}

/**
 * xprt_request_dequeue_transmit_locked - remove a task from the transmission queue
 * @task: pointer to rpc_task
 *
 * Remove a task from the transmission queue
 * Caller must hold xprt->queue_lock
 */
static void
xprt_request_dequeue_transmit_locked(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;

        if (!test_and_clear_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
                return;
        if (!list_empty(&req->rq_xmit)) {
                list_del(&req->rq_xmit);
                if (!list_empty(&req->rq_xmit2)) {
                        struct rpc_rqst *next = list_first_entry(&req->rq_xmit2,
                                        struct rpc_rqst, rq_xmit2);
                        list_del(&req->rq_xmit2);
                        list_add_tail(&next->rq_xmit, &next->rq_xprt->xmit_queue);
                }
        } else
                list_del(&req->rq_xmit2);
}

/**
 * xprt_request_dequeue_transmit - remove a task from the transmission queue
 * @task: pointer to rpc_task
 *
 * Remove a task from the transmission queue
 */
static void
xprt_request_dequeue_transmit(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        spin_lock(&xprt->queue_lock);
        xprt_request_dequeue_transmit_locked(task);
        spin_unlock(&xprt->queue_lock);
}

/**
 * xprt_request_prepare - prepare an encoded request for transport
 * @req: pointer to rpc_rqst
 *
 * Calls into the transport layer to do whatever is needed to prepare
 * the request for transmission or receive.
 */
void
xprt_request_prepare(struct rpc_rqst *req)
{
        struct rpc_xprt *xprt = req->rq_xprt;

        if (xprt->ops->prepare_request)
                xprt->ops->prepare_request(req);
}

/**
 * xprt_request_need_retransmit - Test if a task needs retransmission
 * @task: pointer to rpc_task
 *
 * Test for whether a connection breakage requires the task to retransmit
 */
bool
xprt_request_need_retransmit(struct rpc_task *task)
{
        return xprt_request_retransmit_after_disconnect(task);
}

/**
 * xprt_prepare_transmit - reserve the transport before sending a request
 * @task: RPC task about to send a request
 *
 */
bool xprt_prepare_transmit(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;

        dprintk("RPC: %5u xprt_prepare_transmit\n", task->tk_pid);

        if (!xprt_lock_write(xprt, task)) {
                /* Race breaker: someone may have transmitted us */
                if (!test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
                        rpc_wake_up_queued_task_set_status(&xprt->sending,
                                        task, 0);
                return false;

        }
        return true;
}

void xprt_end_transmit(struct rpc_task *task)
{
        xprt_release_write(task->tk_rqstp->rq_xprt, task);
}

/**
 * xprt_request_transmit - send an RPC request on a transport
 * @req: pointer to request to transmit
 * @snd_task: RPC task that owns the transport lock
 *
 * This performs the transmission of a single request.
 * Note that if the request is not the same as snd_task, then it
 * does need to be pinned.
 * Returns '0' on success.
 */
static int
xprt_request_transmit(struct rpc_rqst *req, struct rpc_task *snd_task)
{
        struct rpc_xprt *xprt = req->rq_xprt;
        struct rpc_task *task = req->rq_task;
        unsigned int connect_cookie;
        int is_retrans = RPC_WAS_SENT(task);
        int status;

        if (!req->rq_bytes_sent) {
                if (xprt_request_data_received(task)) {
                        status = 0;
                        goto out_dequeue;
                }
                /* Verify that our message lies in the RPCSEC_GSS window */
                if (rpcauth_xmit_need_reencode(task)) {
                        status = -EBADMSG;
                        goto out_dequeue;
                }
                if (task->tk_ops->rpc_call_prepare_transmit) {
                        task->tk_ops->rpc_call_prepare_transmit(task,
                                        task->tk_calldata);
                        status = task->tk_status;
                        if (status < 0)
                                goto out_dequeue;
                }
                if (RPC_SIGNALLED(task)) {
                        status = -ERESTARTSYS;
                        goto out_dequeue;
                }
        }

        /*
         * Update req->rq_ntrans before transmitting to avoid races with
         * xprt_update_rtt(), which needs to know that it is recording a
         * reply to the first transmission.
         */
        req->rq_ntrans++;

        connect_cookie = xprt->connect_cookie;
        status = xprt->ops->send_request(req);
        if (status != 0) {
                req->rq_ntrans--;
                trace_xprt_transmit(req, status);
                return status;
        }

        if (is_retrans)
                task->tk_client->cl_stats->rpcretrans++;

        xprt_inject_disconnect(xprt);

        task->tk_flags |= RPC_TASK_SENT;
        spin_lock_bh(&xprt->transport_lock);

        xprt->stat.sends++;
        xprt->stat.req_u += xprt->stat.sends - xprt->stat.recvs;
        xprt->stat.bklog_u += xprt->backlog.qlen;
        xprt->stat.sending_u += xprt->sending.qlen;
        xprt->stat.pending_u += xprt->pending.qlen;
        spin_unlock_bh(&xprt->transport_lock);

        req->rq_connect_cookie = connect_cookie;
out_dequeue:
        trace_xprt_transmit(req, status);
        xprt_request_dequeue_transmit(task);
        rpc_wake_up_queued_task_set_status(&xprt->sending, task, status);
        return status;
}

/**
 * xprt_transmit - send an RPC request on a transport
 * @task: controlling RPC task
 *
 * Attempts to drain the transmit queue. On exit, either the transport
 * signalled an error that needs to be handled before transmission can
 * resume, or @task finished transmitting, and detected that it already
 * received a reply.
 */
void
xprt_transmit(struct rpc_task *task)
{
        struct rpc_rqst *next, *req = task->tk_rqstp;
        struct rpc_xprt *xprt = req->rq_xprt;
        int status;

        spin_lock(&xprt->queue_lock);
        while (!list_empty(&xprt->xmit_queue)) {
                next = list_first_entry(&xprt->xmit_queue,
                                struct rpc_rqst, rq_xmit);
                xprt_pin_rqst(next);
                spin_unlock(&xprt->queue_lock);
                status = xprt_request_transmit(next, task);
                if (status == -EBADMSG && next != req)
                        status = 0;
                cond_resched();
                spin_lock(&xprt->queue_lock);
                xprt_unpin_rqst(next);
                if (status == 0) {
                        if (!xprt_request_data_received(task) ||
                            test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
                                continue;
                } else if (test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
                        task->tk_status = status;
                break;
        }
        spin_unlock(&xprt->queue_lock);
}

static void xprt_add_backlog(struct rpc_xprt *xprt, struct rpc_task *task)
{
        set_bit(XPRT_CONGESTED, &xprt->state);
        rpc_sleep_on(&xprt->backlog, task, NULL);
}

static void xprt_wake_up_backlog(struct rpc_xprt *xprt)
{
        if (rpc_wake_up_next(&xprt->backlog) == NULL)
                clear_bit(XPRT_CONGESTED, &xprt->state);
}

static bool xprt_throttle_congested(struct rpc_xprt *xprt, struct rpc_task *task)
{
        bool ret = false;

        if (!test_bit(XPRT_CONGESTED, &xprt->state))
                goto out;
        spin_lock(&xprt->reserve_lock);
        if (test_bit(XPRT_CONGESTED, &xprt->state)) {
                rpc_sleep_on(&xprt->backlog, task, NULL);
                ret = true;
        }
        spin_unlock(&xprt->reserve_lock);
out:
        return ret;
}

static struct rpc_rqst *xprt_dynamic_alloc_slot(struct rpc_xprt *xprt)
{
        struct rpc_rqst *req = ERR_PTR(-EAGAIN);

        if (xprt->num_reqs >= xprt->max_reqs)
                goto out;
        ++xprt->num_reqs;
        spin_unlock(&xprt->reserve_lock);
        req = kzalloc(sizeof(struct rpc_rqst), GFP_NOFS);
        spin_lock(&xprt->reserve_lock);
        if (req != NULL)
                goto out;
        --xprt->num_reqs;
        req = ERR_PTR(-ENOMEM);
out:
        return req;
}

static bool xprt_dynamic_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
        if (xprt->num_reqs > xprt->min_reqs) {
                --xprt->num_reqs;
                kfree(req);
                return true;
        }
        return false;
}

void xprt_alloc_slot(struct rpc_xprt *xprt, struct rpc_task *task)
{
        struct rpc_rqst *req;

        spin_lock(&xprt->reserve_lock);
        if (!list_empty(&xprt->free)) {
                req = list_entry(xprt->free.next, struct rpc_rqst, rq_list);
                list_del(&req->rq_list);
                goto out_init_req;
        }
        req = xprt_dynamic_alloc_slot(xprt);
        if (!IS_ERR(req))
                goto out_init_req;
        switch (PTR_ERR(req)) {
        case -ENOMEM:
                dprintk("RPC:       dynamic allocation of request slot "
                                "failed! Retrying\n");
                task->tk_status = -ENOMEM;
                break;
        case -EAGAIN:
                xprt_add_backlog(xprt, task);
                dprintk("RPC:       waiting for request slot\n");
                /* fall through */
        default:
                task->tk_status = -EAGAIN;
        }
        spin_unlock(&xprt->reserve_lock);
        return;
out_init_req:
        xprt->stat.max_slots = max_t(unsigned int, xprt->stat.max_slots,
                                     xprt->num_reqs);
        spin_unlock(&xprt->reserve_lock);

        task->tk_status = 0;
        task->tk_rqstp = req;
}
EXPORT_SYMBOL_GPL(xprt_alloc_slot);

void xprt_free_slot(struct rpc_xprt *xprt, struct rpc_rqst *req)
{
        spin_lock(&xprt->reserve_lock);
        if (!xprt_dynamic_free_slot(xprt, req)) {
                memset(req, 0, sizeof(*req));   /* mark unused */
                list_add(&req->rq_list, &xprt->free);
        }
        xprt_wake_up_backlog(xprt);
        spin_unlock(&xprt->reserve_lock);
}
EXPORT_SYMBOL_GPL(xprt_free_slot);

static void xprt_free_all_slots(struct rpc_xprt *xprt)
{
        struct rpc_rqst *req;
        while (!list_empty(&xprt->free)) {
                req = list_first_entry(&xprt->free, struct rpc_rqst, rq_list);
                list_del(&req->rq_list);
                kfree(req);
        }
}

struct rpc_xprt *xprt_alloc(struct net *net, size_t size,
                unsigned int num_prealloc,
                unsigned int max_alloc)
{
        struct rpc_xprt *xprt;
        struct rpc_rqst *req;
        int i;

        xprt = kzalloc(size, GFP_KERNEL);
        if (xprt == NULL)
                goto out;

        xprt_init(xprt, net);

        for (i = 0; i < num_prealloc; i++) {
                req = kzalloc(sizeof(struct rpc_rqst), GFP_KERNEL);
                if (!req)
                        goto out_free;
                list_add(&req->rq_list, &xprt->free);
        }
        if (max_alloc > num_prealloc)
                xprt->max_reqs = max_alloc;
        else
                xprt->max_reqs = num_prealloc;
        xprt->min_reqs = num_prealloc;
        xprt->num_reqs = num_prealloc;

        return xprt;

out_free:
        xprt_free(xprt);
out:
        return NULL;
}
EXPORT_SYMBOL_GPL(xprt_alloc);

void xprt_free(struct rpc_xprt *xprt)
{
        put_net(xprt->xprt_net);
        xprt_free_all_slots(xprt);
        kfree_rcu(xprt, rcu);
}
EXPORT_SYMBOL_GPL(xprt_free);

static void
xprt_init_connect_cookie(struct rpc_rqst *req, struct rpc_xprt *xprt)
{
        req->rq_connect_cookie = xprt_connect_cookie(xprt) - 1;
}

static __be32
xprt_alloc_xid(struct rpc_xprt *xprt)
{
        __be32 xid;

        spin_lock(&xprt->reserve_lock);
        xid = (__force __be32)xprt->xid++;
        spin_unlock(&xprt->reserve_lock);
        return xid;
}

static void
xprt_init_xid(struct rpc_xprt *xprt)
{
        xprt->xid = prandom_u32();
}

static void
xprt_request_init(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_xprt;
        struct rpc_rqst *req = task->tk_rqstp;

        req->rq_timeout = task->tk_client->cl_timeout->to_initval;
        req->rq_task    = task;
        req->rq_xprt    = xprt;
        req->rq_buffer  = NULL;
        req->rq_xid     = xprt_alloc_xid(xprt);
        xprt_init_connect_cookie(req, xprt);
        req->rq_snd_buf.len = 0;
        req->rq_snd_buf.buflen = 0;
        req->rq_rcv_buf.len = 0;
        req->rq_rcv_buf.buflen = 0;
        req->rq_snd_buf.bvec = NULL;
        req->rq_rcv_buf.bvec = NULL;
        req->rq_release_snd_buf = NULL;
        xprt_reset_majortimeo(req);
        dprintk("RPC: %5u reserved req %p xid %08x\n", task->tk_pid,
                        req, ntohl(req->rq_xid));
}

static void
xprt_do_reserve(struct rpc_xprt *xprt, struct rpc_task *task)
{
        xprt->ops->alloc_slot(xprt, task);
        if (task->tk_rqstp != NULL)
                xprt_request_init(task);
}

/**
 * xprt_reserve - allocate an RPC request slot
 * @task: RPC task requesting a slot allocation
 *
 * If the transport is marked as being congested, or if no more
 * slots are available, place the task on the transport's
 * backlog queue.
 */
void xprt_reserve(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_xprt;

        task->tk_status = 0;
        if (task->tk_rqstp != NULL)
                return;

        task->tk_status = -EAGAIN;
        if (!xprt_throttle_congested(xprt, task))
                xprt_do_reserve(xprt, task);
}

/**
 * xprt_retry_reserve - allocate an RPC request slot
 * @task: RPC task requesting a slot allocation
 *
 * If no more slots are available, place the task on the transport's
 * backlog queue.
 * Note that the only difference with xprt_reserve is that we now
 * ignore the value of the XPRT_CONGESTED flag.
 */
void xprt_retry_reserve(struct rpc_task *task)
{
        struct rpc_xprt *xprt = task->tk_xprt;

        task->tk_status = 0;
        if (task->tk_rqstp != NULL)
                return;

        task->tk_status = -EAGAIN;
        xprt_do_reserve(xprt, task);
}

static void
xprt_request_dequeue_all(struct rpc_task *task, struct rpc_rqst *req)
{
        struct rpc_xprt *xprt = req->rq_xprt;

        if (test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate) ||
            test_bit(RPC_TASK_NEED_RECV, &task->tk_runstate) ||
            xprt_is_pinned_rqst(req)) {
                spin_lock(&xprt->queue_lock);
                xprt_request_dequeue_transmit_locked(task);
                xprt_request_dequeue_receive_locked(task);
                while (xprt_is_pinned_rqst(req)) {
                        set_bit(RPC_TASK_MSG_PIN_WAIT, &task->tk_runstate);
                        spin_unlock(&xprt->queue_lock);
                        xprt_wait_on_pinned_rqst(req);
                        spin_lock(&xprt->queue_lock);
                        clear_bit(RPC_TASK_MSG_PIN_WAIT, &task->tk_runstate);
                }
                spin_unlock(&xprt->queue_lock);
        }
}

/**
 * xprt_release - release an RPC request slot
 * @task: task which is finished with the slot
 *
 */
void xprt_release(struct rpc_task *task)
{
        struct rpc_xprt *xprt;
        struct rpc_rqst *req = task->tk_rqstp;

        if (req == NULL) {
                if (task->tk_client) {
                        xprt = task->tk_xprt;
                        xprt_release_write(xprt, task);
                }
                return;
        }

        xprt = req->rq_xprt;
        if (task->tk_ops->rpc_count_stats != NULL)
                task->tk_ops->rpc_count_stats(task, task->tk_calldata);
        else if (task->tk_client)
                rpc_count_iostats(task, task->tk_client->cl_metrics);
        xprt_request_dequeue_all(task, req);
        spin_lock_bh(&xprt->transport_lock);
        xprt->ops->release_xprt(xprt, task);
        if (xprt->ops->release_request)
                xprt->ops->release_request(task);
        xprt->last_used = jiffies;
        xprt_schedule_autodisconnect(xprt);
        spin_unlock_bh(&xprt->transport_lock);
        if (req->rq_buffer)
                xprt->ops->buf_free(task);
        xprt_inject_disconnect(xprt);
        xdr_free_bvec(&req->rq_rcv_buf);
        xdr_free_bvec(&req->rq_snd_buf);
        if (req->rq_cred != NULL)
                put_rpccred(req->rq_cred);
        task->tk_rqstp = NULL;
        if (req->rq_release_snd_buf)
                req->rq_release_snd_buf(req);

        dprintk("RPC: %5u release request %p\n", task->tk_pid, req);
        if (likely(!bc_prealloc(req)))
                xprt->ops->free_slot(xprt, req);
        else
                xprt_free_bc_request(req);
}

#ifdef CONFIG_SUNRPC_BACKCHANNEL
void
xprt_init_bc_request(struct rpc_rqst *req, struct rpc_task *task)
{
        struct xdr_buf *xbufp = &req->rq_snd_buf;

        task->tk_rqstp = req;
        req->rq_task = task;
        xprt_init_connect_cookie(req, req->rq_xprt);
        /*
         * Set up the xdr_buf length.
         * This also indicates that the buffer is XDR encoded already.
         */
        xbufp->len = xbufp->head[0].iov_len + xbufp->page_len +
                xbufp->tail[0].iov_len;
}
#endif

static void xprt_init(struct rpc_xprt *xprt, struct net *net)
{
        kref_init(&xprt->kref);

        spin_lock_init(&xprt->transport_lock);
        spin_lock_init(&xprt->reserve_lock);
        spin_lock_init(&xprt->queue_lock);

        INIT_LIST_HEAD(&xprt->free);
        xprt->recv_queue = RB_ROOT;
        INIT_LIST_HEAD(&xprt->xmit_queue);
#if defined(CONFIG_SUNRPC_BACKCHANNEL)
        spin_lock_init(&xprt->bc_pa_lock);
        INIT_LIST_HEAD(&xprt->bc_pa_list);
#endif /* CONFIG_SUNRPC_BACKCHANNEL */
        INIT_LIST_HEAD(&xprt->xprt_switch);

        xprt->last_used = jiffies;
        xprt->cwnd = RPC_INITCWND;
        xprt->bind_index = 0;

        rpc_init_wait_queue(&xprt->binding, "xprt_binding");
        rpc_init_wait_queue(&xprt->pending, "xprt_pending");
        rpc_init_wait_queue(&xprt->sending, "xprt_sending");
        rpc_init_priority_wait_queue(&xprt->backlog, "xprt_backlog");

        xprt_init_xid(xprt);

        xprt->xprt_net = get_net(net);
}

/**
 * xprt_create_transport - create an RPC transport
 * @args: rpc transport creation arguments
 *
 */
struct rpc_xprt *xprt_create_transport(struct xprt_create *args)
{
        struct rpc_xprt *xprt;
        struct xprt_class *t;

        spin_lock(&xprt_list_lock);
        list_for_each_entry(t, &xprt_list, list) {
                if (t->ident == args->ident) {
                        spin_unlock(&xprt_list_lock);
                        goto found;
                }
        }
        spin_unlock(&xprt_list_lock);
        dprintk("RPC: transport (%d) not supported\n", args->ident);
        return ERR_PTR(-EIO);

found:
        xprt = t->setup(args);
        if (IS_ERR(xprt)) {
                dprintk("RPC:       xprt_create_transport: failed, %ld\n",
                                -PTR_ERR(xprt));
                goto out;
        }
        if (args->flags & XPRT_CREATE_NO_IDLE_TIMEOUT)
                xprt->idle_timeout = 0;
        INIT_WORK(&xprt->task_cleanup, xprt_autoclose);
        if (xprt_has_timer(xprt))
                timer_setup(&xprt->timer,
                                xprt_init_autodisconnect,
                                TIMER_DEFERRABLE);
        else
                timer_setup(&xprt->timer, NULL, 0);

        if (strlen(args->servername) > RPC_MAXNETNAMELEN) {
                xprt_destroy(xprt);
                return ERR_PTR(-EINVAL);
        }
        xprt->servername = kstrdup(args->servername, GFP_KERNEL);
        if (xprt->servername == NULL) {
                xprt_destroy(xprt);
                return ERR_PTR(-ENOMEM);
        }

        rpc_xprt_debugfs_register(xprt);

        dprintk("RPC:       created transport %p with %u slots\n", xprt,
                        xprt->max_reqs);
out:
        return xprt;
}

static void xprt_destroy_cb(struct work_struct *work)
{
        struct rpc_xprt *xprt =
                container_of(work, struct rpc_xprt, task_cleanup);

        rpc_xprt_debugfs_unregister(xprt);
        rpc_destroy_wait_queue(&xprt->binding);
        rpc_destroy_wait_queue(&xprt->pending);
        rpc_destroy_wait_queue(&xprt->sending);
        rpc_destroy_wait_queue(&xprt->backlog);
        kfree(xprt->servername);
        /*
         * Tear down transport state and free the rpc_xprt
         */
        xprt->ops->destroy(xprt);
}

/**
 * xprt_destroy - destroy an RPC transport, killing off all requests.
 * @xprt: transport to destroy
 *
 */
static void xprt_destroy(struct rpc_xprt *xprt)
{
        dprintk("RPC:       destroying transport %p\n", xprt);

        /*
         * Exclude transport connect/disconnect handlers and autoclose
         */
        wait_on_bit_lock(&xprt->state, XPRT_LOCKED, TASK_UNINTERRUPTIBLE);

        del_timer_sync(&xprt->timer);

        /*
         * Destroy sockets etc from the system workqueue so they can
         * safely flush receive work running on rpciod.
         */
        INIT_WORK(&xprt->task_cleanup, xprt_destroy_cb);
        schedule_work(&xprt->task_cleanup);
}

static void xprt_destroy_kref(struct kref *kref)
{
        xprt_destroy(container_of(kref, struct rpc_xprt, kref));
}

/**
 * xprt_get - return a reference to an RPC transport.
 * @xprt: pointer to the transport
 *
 */
struct rpc_xprt *xprt_get(struct rpc_xprt *xprt)
{
        if (xprt != NULL && kref_get_unless_zero(&xprt->kref))
                return xprt;
        return NULL;
}
EXPORT_SYMBOL_GPL(xprt_get);

/**
 * xprt_put - release a reference to an RPC transport.
 * @xprt: pointer to the transport
 *
 */
void xprt_put(struct rpc_xprt *xprt)
{
        if (xprt != NULL)
                kref_put(&xprt->kref, xprt_destroy_kref);
}
EXPORT_SYMBOL_GPL(xprt_put);